It's an easy run after a long (or particularly tough) run to help your muscles recover.
A recovery run will help wipe the lactic acid from your muscles and therefore reduce muscle trauma and speed recovery and muscle regrowth.

"If trees could scream, would we be so cavalier about cutting them down? We might, if they screamed all the time, for no good reason." J. Handy

I think it's just another way of saying "really easy" with the emphasis that you did something hard the day before so you need a break.
Also, dutchie, I love your quote about when you go running. Makes me laugh every time I see it.

So, me not running the day after my long run is not a good thing? I thought I was supposed to give my legs a rest.
How long does this recovery run have to be? Or doesn't it matter? Is it just meant to warm up the legs and get the blood flow going?
Sean: if the quote makes you laugh, have you ever taken a good look at my avatar?

Dutchie I go running in the early morning, before my brain figures out what I'm up to.

So, me not running the day after my long run is not a good thing? I thought I was supposed to give my legs a rest.
How long does this recovery run have to be? Or doesn't it matter? Is it just meant to warm up the legs and get the blood flow going?

Rest is definitely a good thing. I think a lot of the hard core guys will typically include recovery runs.
You've got it right though, if you're going to go out after a long/tough run the previous day, take it easy. Just move the legs, get the blood flowing.

"If trees could scream, would we be so cavalier about cutting them down? We might, if they screamed all the time, for no good reason." J. Handy

How long does this recovery run have to be? Or doesn't it matter? Is it just meant to warm up the legs and get the blood flow going?

I think of recovery runs as being 3~4 really easy light miles with no concerns about pace, though intensity will vary based on what you're recovering from.
You're absolutely right about the blood flow thing. I've read in more than one place that if you can do it, your post-race recovery will be much better if your suck it up and do the recovery run the day after the race, and then take a day off. Even in the case of a marathon.

On your deathbed, you won't wish that you'd spent more time at the office. But you will wish that you'd spent more time running. Because if you had, you wouldn't be on your deathbed.

I dont even think it needs to be that long...I went for my long run last weekend and then went to buy shoes after. Maybe about 3-4 hours after Over the course of trying on 7-8 pairs (I wanted a change) I probably ran about a mile on the tread, maybe a bit more. All in 1-2 minute increments. My legs completely loosened up and felt great after that. I wouldnt mind having a treadmill or elliptical in my house for that...but sigh, no room

I have become Death, the destroyer of electronic gadgets

"When I got too tired to run anymore I just pretended I wasnt tired and kept running anyway" - dd, age 7